The present invention relates to tunable bandpass-bandreject filters in general, and in particular to a multiple-feedback-path filter having a single variable tuning element and exhibiting little change in Q (quality factor) over a predetermined frequency range.
Multiple-feedback-path filters are well known in the art, and are used in a variety of active filter applications, including bandpass and bandreject (notch) functions. One of the more widely used multiple-feedback-path filters is the tunable active RC filter because a good Q may be achieved and maintained constant over a broad frequency range. Since the Q of a filter is a function of the frequency and the passive resistive (R) and capacitance (C) elements, however, constant-Q performance has previously required two or more ganged variable elements.